On the study of parylene-N for millimeter-wave integrated circuits

In this work Parylene-N is investigated as a passivation layer for microwave and millimeter-wave integrated circuits (MMIC). The electrical and mechanical properties of this material show great potential for various applications in integrated circuits especially at higher frequencies. For the first time, Parylene-N has been used as a passivation layer on different test structures and their performance is studied up to 40GHz. The measurement results obtained from ring resonators and Coplanar Waveguide (CPW) transmission lines before and after passivation show that a 10 μm thick Parylene-N layer increases the insertion loss by only a negligible amount (0.007dB/mm at 40GHz), while a 5 μm thick coating does not have any influence on the insertion loss, confirming that the loss tangent of this coating material is very low. Besides, in measuring the resonance frequencies of different ring resonators a frequency shift of less than 1% is observed with a 10 μm passivation at 40GHz, while the shift is less than 0.05% for a 5 μm thickness, indicating a very low dielectric constant. In this paper we also show the performance of a multi-layer structure using a Coplanar Waveguide (CPW) vertical transition with vias etched between two Parylene-N layers. The results demonstrate the ability to use this flexible material as a low loss multi-layer substrate for microwave frequency applications. Finally a humidity study is performed by employing an array of dewpoint sensors with 10 μm thick Parylene-N coating. Hence the Mean Time to Failure (MTTF) under different humidity and temperature conditions is derived. Results indicate that Parylene-N is a good candidate as an encapsulant for MMIC applications.